US3731592A

US3731592A - Valving mechanism for hydraulic storage means, especially for hydraulic testing apparatus

Info

Publication number: US3731592A
Application number: US00205957A
Authority: US
Inventors: H Kreiskorte
Original assignee: Carl Schenck Maschinenfabrik GmbH
Current assignee: Carl Schenck AG
Priority date: 1971-10-28
Filing date: 1971-12-08
Publication date: 1973-05-08
Anticipated expiration: 1990-05-08
Also published as: DE2153749C2; DE2153749B1; DE2153749A1

Abstract

The present valving mechanism forms part of the load piston cylinder means, for example, of a hydraulic testing apparatus. The load cylinder is provided with a first control inlet at each end thereof and a second control inlet substantially at each end of the resonant stroke of the piston. Storage means are connected to the load cylinder also substantially at each end of said resonant stroke. Further, control ring pistons are slideably arranged on the piston rod on each side of a piston which is fixed to the rod. The control ring pistons close or open the ports to said storage means.

Description

United States Patent 1 Kreiskorte [75] Inventor: Heinz Kreiskorte, Post Dortmundl-loerder, Germany [73] Assignee: Carl Schenck Masehinenlabrik Gmhl-l, Darmstadt, Germany [22] Filed: Dec. 8, 1971 [21] Appl. No.: 205,957

[30] Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 2,415,783 2/1947 Bassett et al ..92/65 X 1 May 8, 1973 2,506,374 5/1950 McMahon ..92/65 X 2,806,449 9/1957 Simmons ..91/411 A X 3,312,146 4/1967 Quere et al. ..92/65 X FOREIGN PATENTS OR APPLICATIONS 2,023,268 11/1970 Germany ..91/167 Primary ExaminerMartin P. Schwadron Assistant Examiner-Allen M. Ostrager Attorney-Wolfgang G. Fasse [5 7] ABSTRACT The present valving mechanism forms part of the load piston cylinder means, for example, of a hydraulic testing apparatus. The load cylinder is provided with a first control inlet at each end thereof and a second control inlet substantially at each end of the resonant stroke of the piston. Storage means are connected to the load cylinder also substantially at each end of said resonant stroke. Further, control ring pistons are slideably arranged on the piston rod on each side of a piston which is fixed to the rod. The control ring pistons close or open the ports to said storage means.

6 Claims, 2 Drawing Figures MUVEMENT SENSOR WEIGHTS ./4

PATENTEI] HAY 81975 SHEET 1 UF 2 MOVEMENT SENSOR WEIGHTS FIG! PATENTEU W 75 SHEET 2 BF 2 MOVEMENT SENSOR CONTR L UN T S T H m E W FIGZ VALVING MECHANISM FOR HYDRAULIC STORAGE MEANS, ESPECIALLY FOR HYDRAULIC TESTING APPARATUS BACKGROUND OF THE INVENTION The present invention relates to a valving mechanism for hydraulic storage means, especially for hydraulic testing apparatus. Such machines include a first hydraulic piston cylinder arrangement for producing a dynamic, varying load preferably at the resonance frequency of the apparatus or system, and a second piston cylinder arrangement for producing an initial load on which the dynamic varying load is superimposed. The two cylinder piston arrangements may also be operated to produce a testing load conforming to a predetermined load characteristic. The latter mode of operation may also be referred to as a so called slow speed drive.

These hydraulic testing machines or systems are adapted for a switch over between the so called resonance operation and the so called slow speed drive as mentioned above. The two hydraulic cylinders are connected to the means which receive or hold the probe which is to be tested mechanically. One of the cylinders produces the dynamically varying load during the so called resonance operation. The other cylinder serves for producing a so called initial load upon which there is superimposed the oscillating load produced by the resonance cylinder. In this manner, for example, it is possible to convert a pure osciilating load into a pulsating load. In this type of operation, the piston of the second hydraulic cylinder piston arrangement, the so called initial load piston cylinder arrangement, is subjected to loads on both of its surfaces and thus it follows the oscillating movements produced by the first or resonant piston cylinder arrangement. In order to enable, the second piston to make the just-mentioned movements, it is necessary that the pressure medium on both sides of the piston in the cylinder is connected to a respective hydraulic storage which is cable of temporarily receiving the displaced volume of pressure medium.

On the other hand, when the system is to operate in the above-mentioned slow speed drive manner, the second or initial load piston cylinder arrangement performs another function if, for example, a testing load having a predetermined load characteristic is to be applied to the sample to be tested, however, without a superimposed oscillating load. In this type of operation the hydraulic storage spaces connected to each side, that is, to the cylinder spaces above and below the second piston would interfere with the desired slow speed drive. Accordingly, it is necessary to close off these storage means for the slow speed drive operation.

The closing and opening of the conduits connecting the hydraulic storage and the cylinder of the second piston cylinder arrangement could be accomplished by valves arranged in said conduits whereby the valves must be actuated either by hand or by remote control. Providing additional valves of course increases the costs and besides it requires a separate or additional control step from actuating these valves when the system is to be switched for one type of operation to the other as described above. Anotherdisadvantage of valves in saidconduits is seen in that thevalves act as throttle means in the conduit so that the flow of the pressure medium is dampened as it passes through these valves. Such dampening is particularly disadvantageous because it prevents accomplishing a large resonance rise or at least impedes the attaining of such rise.

OBJECTS OF THE INVENTION In view of the above, it is the aim of the invention to achieve the following objects singly or in combination:

to overcome the above-outlined drawbacks, more specifically to provide a valving mechanism which is simple in construction and, so to speak, blends into the piston cylinder arrangements employed in hydraulic testing systems as described above;

to provide a valving mechanism which may be automatically operated simultaneously with the switching of a testing apparatus from one mode of operation to another so that no special actuating means are necessary;

to substantially eliminate a throttling action in the conduits connecting a hydraulic storage means to the cylinder of a piston cylinder arrangement, especially in a hydraulic testing system;

to assure the desired, substantial resonance rise when the machine operates in the resonance mode, by eliminating features which impede such high resonance rise.

SUMMARY OF THE INVENTION According to the invention there is provided a valving mechanism for hydraulic storage means, especially for hydraulic testing systems, wherein the second cylinder which is connected to said storage means through respective ports in its cylinder wall and wherein a piston rod which has rigidly attached thereto a piston slideable back and forth within said cylinder, is also provided with ring pistons one of which is slideable on said piston rod on each side of said first-mentioned piston. The cylinder is provided with control ports at its ends as well as substantially at .each end of the reciprocating resonance movement of the piston, whereby upon opening of the control ports at the end of the cylinder, the ring pistons are moved to abut against said piston and thereby close said ports to the storage means. On the other hand, when the control ports adjacent to the end of the reciprocating resonance movement are opened, the ring pistons are moved away from said first-mentioned piston toward the respective end of the cylinder whereby said ports to the storage means are opened.

Preferably, the ring pistons are provided with sealing means around their circumferential surface. These sealing means are preferably arranged adjacent the end of the respective ring piston which faces away from said first-mentioned piston.

BRIEF F IGURE'DESCRIPT ION In order that the invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 illustrates a schematic diagram of a hydraulic testing machine whereby the hydraulic as well as the electric circuits have been simplified for claritys sake, said machine being capable of producing a dynamic alternating load with an initial load which constitute the testing load and wherein the arrangement is shown in the position for the resonance mode of operation; and

FIG. 2 is a diagram similar to that of FIG. 1 but illustrating the arrangement for subjecting the test sample to static loads or to a testing load having a predetermined, slowly varying load characteristic.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS A sample 1 to be tested, for example a tensile rod is secured at one end thereof to a load cell 2 which in turn is secured to the machine frame 3 shown in simplified fashion. The machine frame 3 supports all the members of the hydraulic testing system. The other end of the sample 1 to be tested is secured to a mass 4 which in turn is connected to a piston rod 5. The piston rod 5 has secured thereto a piston 6 which slides up and down or back and forth in a cylinder 7 which constitutes the so called means force cylinder. The just-described piston cylinder arrangement comprising the

elements

5, 6, and 7 constitutes the second piston cylinder arrangement of the system. The first piston cylinder arrangement of the system comprises a piston rod 9, a piston 10, and a cylinder 11. The piston rod 9 and the piston rod 5 are connected to each other through an intermediate member 8. The upper end of the piston rod 9 is operatively connected to a movement sensing member 12.

A conventional source of hydraulic power (not shown) is connected to the first cylinder 11 through hydraulic conduits 13. The flow of pressure medium through the conduits 13 is controlled by a servo-valve 14 as well as by a hydraulic switching valve 15 in such a manner that the piston 10 is alternately subjected to pressure. In other words, first one surface of the piston 10 is subjected to pressure to move the piston 10 and its rod 9 in one direction and then the opposite surface of the piston 10 is subjected to pressure to move it in the opposite direction together with its piston rod and so forth. Thus, a sinusoidal, oscillating load is applied to the sample 1 to be tested.

In order to accomplish the above sinusoidally oscillating load on the piston 10, the servo-valve 14 is controlled by a central control unit 16 in response to the movement sensor 12 and preferably through an amplifier 17 in such a manner that each of the two hydraulic conduits 13 are alternately connected to the source of hydraulic pressure.

In order to superimpose an initial or mean load on the dynamic load which oscillates about a zero value and which, as mentioned, is produced by the first piston cylinder arrangement 9, l0, 11, the piston 6 which is rigidly secured to its piston rod 5 may be subjected on one of its surfaces by hydraulic fluid either under a predetermined constant pressure or a pressure which varies relatively slowly. For this purpose the second cylinder is provided with a pair of first control ports 18 located approximately at the points of return of the reciprocating stroke of the piston 6. These control ports 18 are connected to respective hydraulic conduits for the supply and removal of hydraulic liquid. The term reciprocating stroke" designates the movement of the piston 6 in response to the resonance movement of the piston 10. Such reciprocating movement must be distinguished from the movement of the piston 6 which the piston 6 performs during the so called slow motion mode of operation. The slow motion movement has a stroke which is substantially longer than said stroke during resonance operation.

As mentioned above, FIG. 1 depicts said resonant mode of operation. In the position in which the control valve 19 is shown in FIG. 1, the hydraulic conduits 20 which are connected to the control ports 18 of the cylinder 7 are interconnected with further conduits 21 and through these conduits through

respective servovalves

22 and 23 to the source of hydraulic pressure not shown. The servo-

valves

22 and 23 are controlled through amplifiers 24 also by the control unit 16 in such a manner that one of the two surfaces of the piston 6 is subjected to the desired pressure.

The volume or rather the cylinder volumes adjacent to each side or surface of the piston 6 varies very rapidly with each cycle of oscillation because the piston 6 performs a rapid oscillatory motion in response to the respective oscillatory motion of the piston 10 in the resonance cylinder 11. It is not possible to open and close the hydraulic conduits 20 in an equally rapid manner. Therefore, the volume above the piston 6 and the volume below the piston 6 are connected to respective hydraulic storage means 26. For this purpose there are provided connecting ports 25 which are located in the wall of the cylinder 7 about at each end of the reciprocatory movement or stroke of the piston 6. In other words, these connecting ports 25 are located at about the return point of said reciprocatory movement of the piston 6. These storage means 26 receive the pressure medium volume which is temporarily displaced due to the oscillatory movements of the piston 6.

FIG. 2 is a circuit diagram illustrating the so called slow speed drive. In this mode of operation, the sample 1 to be tested is to be subjected to static loads or to a slowly varying load or load change. For this purpose the hydraulic drive for the resonance cylinder 11 has been switched off by means of the switching valve 15. Moreover, the control or switching valve 19 has been actuated in such a manner that the control ports 27, one of which is provided at each end of the second cylinder 7, are now connected through respective hydraulic conduits 28 to the source of hydraulic pres sure.

According to the invention, there is arranged a ring piston 29 on each side of the piston 6 of the mean load cylinder 7. These ring pistons 29 are slideable back and fourth along the respective portion of the piston rod 6. These ring pistons 29 provide a seal relative to the inner wall of the cylinder 7. Such seal may be even improved by sealing rings 30 to be described in more detail below.

In the so called resonance mode of operation, as described above, with reference to FIG. 1, the ring pistons 29 are located adjacent to the respective end of the cylinder 7 because the surfaces of the ring pistons 29 which face the piston 6 are subjected to the pressure medium through the control port 18. However, if, as shown in FIG. 2, representing the slow drive mode of operation, the pressure medium is admitted through the control openings 27 at the ends of the cylinder 7, the surfaces of the ring pistons 29 which face the respective end of the cylinder 7 are subjected to said pressure medium whereby these ring pistons 29 are pressed against the pistons 6. In this position the ring pistons 29 close the connecting ports 25 to the storage means 26 as well as the control ports 18 which may also be referred to as inlet or outlet control ports.

The closing of the connecting ports 25 to the storage means 26 is necessary during the so called slow drive mode of operation in order to avoid that the storage means 26 act as dead space.

In view of the foregoing, it will be appreciated that according to the invention the switching over from one of the two possible modes of operation such as the resonance mode of operation or the slow drive mode of operation to the other mode of operation is accomplished simply by switching the two control or switching valves and 19. The opening or closing of the respective pressure medium ports in the cylinder 7, especially of the connecting port for the storage means 26 is accomplished automatically by the shifting of the ring pistons 29 in response to the pressure medium. This constitutes a substantial advance in the art as compared to other devices for closing the respective pressure medium ports for example, by means of valves or the like because the ring pistons 29 have the advantage that they may be produced relatively easily. Besides, there are no special means required for keeping the ring pistons 29 in their end positions. Another very sub stantial advantage is seen in that the ports to the storage means 26 provide an unimpeded connection between the inner space of the cylinder 7 and the respective storage means 26 which connection is free of disadvantageous throttling. Thus, the pressure drop between the storage 26 and the cylinder 7 is rather small which has the important advantage that a large resonance rise is possible during resonance operation.

Another advantage of the invention is seen in that during the so called slow drive mode of operation large strokes of the piston 6 are possible without any danger that the control ports 18 and the connecting ports 25 are opened. This is so because, according to the invention, the control ports 27 which control said slow drive mode of operation are arranged at the ends of the cylinder 7 and because the ring pistons 29 as may be seen from the diagrammatic showing of the drawings, may have a substantial axial height. Moreover, for further facilitating the closing of the

ports

18 and 25 during the slow drive mode of operation, the invention provides the ring pistons 29 with sealing rings 30 which are arranged preferably at the outer ends of the ring pistons 29 that is, these sealing rings 30 are preferably arranged adjacent to the ring piston end face which faces toward the respective end of the cylinder 7. This position of the sealing rings 30 at the outer ends of the ring pistons 29 has the further advantage that the ring pistons 29 will be positively moved away from the piston 6 upon admission of pressure medium through the ports 18 even if the ports 18, as may be seen in FIG. 2, are not located in a plane defined by the contact between the surfaces of the piston 6 and the ring pistons 29. It will be noted that the ports 18 are located slightly above and below the just-mentioned planes.

The arrangement of the

ports

18 and 25 approximately at the ends of the point of return of the piston 6, as mentioned above, is determined only by the length of the oscillating stroke during the resonance mode of operation in which situation the ring pistons 29 are located at their respective ends of the cylinder 7. in other words, when the ring pistons 29 are in their end position remote from the piston 6, they must not close the

ports

18 and 25. The stroke performed by the piston 6 and thus by the ring pistons 29 during the slow drive mode of operation has no influence on the position of the

ports

18 and 25 and, also as mentioned, the stroke during said slow drive mode of operation may be substantially larger than the oscillating stroke during the resonance mode of operation.

The pressure storage means 26 may be of conventional structure, for example, these storage means may contain a compressable gas which is separated from the pressure liquid by a membrane.

The central control unit 16 receives its input signals from the movement sensor 12 and also from the load cell 2. However, in addition, the central control unit may provide further control signals, for example, so called follow up signals which determine the load characteristic at the hydraulic cylinder 7. Further, the central control unit 16 may have stored therein a complete program for controlling the testing system.

Although the invention has been described with reference to specific example embodiments, especially example mode of operations, it is to be understood that it is intended to cover all modifications and equivalents within the scope of the appended claims.

What is claimed is:

1. A valving mechanism for hydraulic storage means, comprising a first hydraulic piston cylinder arrangement including a first cylinder, a first piston rod, a first piston rigidly secured to said first piston rod for sliding in said first cylinder, and control ports in said first cylinder on either side of said first piston, a second piston cylinder arrangement including a second cylinder, a second piston rod, a second piston rigidly secured to said second piston rod for sliding reciprocation in said second cylinder between return points, first control port means at each end of said second cylinder, second control port means in said second cylinder intermediate its ends and about adjacent to said return points of reciprocation of said second piston, third port means in said second cylinder, hydraulic storage means, conduit means for connecting said hydraulic storage means to said third port means, ring piston means slideably located on said second piston rod and on each side of said second piston whereby upon opening of said first control port means the ring piston means are located adjacent to said second piston for closing said third ports to said hydraulic storage means, whereas upon opening of said second control port means the ring piston means are located remote from said second piston means for opening said third ports, and means for interconnecting said first and second piston rods.

2. The valving mechanism according to claim 1, wherein each of said ring piston means comprises sealing means around its circumference for providing a seal relative to said second cylinder.

3. The valving mechanism according to claim 2, wherein said sealing means are located adjacent to an end of the respective ring piston means which end is remote from said second piston.

from said piston and closed when said ring piston means are located adjacent to said piston.

S. The valving mechanism according to claim 4, wherein each of said ring piston means comprises sealing means around its circumference for providing a seal relative to said cylinder.

6. The valving mechanism according to claim 5, wherein said sealing means are located adjacent to an end of the respective ring piston means which end is remote from said piston.

Claims

4. A hydraulic valving mechanism comprising a cylinder, a piston rod, a piston rigidly secured to said piston rod for slideable reciprocation in said cylinder, ring piston means slideable on said piston rod on each side of said piston, first control ports at each end of said cylinder, second control ports intermediate the ends of said cylinder and about adjacent to points of return of said piston reciprocation, and third ports also located substantially adjacent to said points of return of said piston reciprocation whereby said third ports are opened when the ring piston means are located remote from said piston and closed when said ring piston means are located adjacent to said piston.

5. The valving mechanism according to claim 4, wherein each of said ring piston means comprises sealing means around its circumference for providing a seal relative to said cylinder.